Kit Harington, the English actor who plays the morally forthright Jon Snow on HBO’s “Game of Thrones,” was showing a guest around the Northern Ireland set where he was spending a September evening battling a traitor, when he paused to note the grim decor that so often crops up on the series.

“There’s always heads on pikes,” Harington said nonchalantly.

It was early last fall when Harington was shooting the sequence that would appear in the fifth episode of the show’s fourth season, which saw him confront the Night’s Watch mutineers hiding out at Craster’s Keep — and if you missed the installment, titled “First of His Name,” you might want to stop reading now.

The episode, which aired Sunday, saw Jon bring a squad of his sworn brothers north of the wall on a mission to punish them for their desertion and to ensure they would not be able to reveal the secrets of Castle Black to the invading Wildings and their king, Mance Rayder (Ciaran Hinds). On the set, which was constructed on the pastoral Clandeboye Estate, a placid locale famed for its dairy products and its wedding receptions, Harington rehearsed the choreography of the standoff with Burn Gorman’s wicked Karl Tanner.

“It’s been a really incredible set to look at but a really inhospitable place to work,” Harington said. “You’ve always got dead pig that’s burning. In ‘Thrones,’ they use everything that’s real, so you’ve got a very warm heated environment — somehow we’re always shooting in summer. I’ve always got blood on my face and it’s made out of sugar syrup, so wasps fly at your face during scenes. Doing a sword fight in there, as I found out today, is a bit of a task. You come outside to get fresh air and the wasps attack your face. You go back inside and you’re choking on smoke and dead pig smell.

“There’s that old cliché of acting isn’t that glamorous, but I think if anything’s proved it it’s when we’re working extremely long days – and we all love it …. It’s tough, it’s grueling, but it makes it because you’re in that world, especially my bits, you’re always hot and sweaty and muddy and dirty and it sort of infects the whole scene.”

Clad in his Night’s Watch blacks, Harington smoked between scenes, enjoying the fresh air of the September night before being called back to the close quarters of the set, where he and Gorman would spar for the cameras over and over again for director Michelle MacLaren (though Harington made a point of asking his scene partner to take it easy on the ankle he injured in a 2012 fall).

“It’s a pretty heavy fight, this,” the actor said during one of the breaks. “Actually, I think it’s the most complex one we’ve done or definitely that I’ve done on ‘Thrones.’ It’s in a confined space, and it’s a longsword versus two short daggers and we didn’t have a huge amount of time to rehearse. So it’s becoming doing it on the hoof, but it’s a very important fight in the story.”

Kit Harington in a scene from “Game of Thrones.” (Helen Sloan / HBO)

Harington, who had only acted on stage before landing the marquee role in the series adapted from George R.R. Martin’s best-selling novels, did point out that he enjoys filming the sword fights and feels that he’s become more adept at such sequences since the first season. It still isn’t exactly easy to wield a longsword — in this case, Longclaw, the weapon forged from Valyrian Steel gifted to Jon by the late Lord Commander Jeor Mormont.

The version of the weapon Harington carried was made of light aluminum, and as he fought with Gorman, he not only had to remember specific moves but also to accurately represent the weight of the blade.

“It’s incredibly difficult, sword fight scenes, they really are tricky,” he said. “I’ve done a lot of them now. There’s nothing quite like the adrenaline you get just before you’re about to do a fight because you know as safe as you can make it, there’s always something that can go wrong. It puts you on edge, which makes a sword fight what it is – again, the real environment creates the scene in a way. You have so much to remember with a sword fight: All through it you’ve got to be acting; you can’t just be remembering the moves, you’ve got to be in the moment, as it were.”

Of course, Snow is wrestling with more than just bloodthirsty adversaries this season. The physical battles are sometimes the easier ones, Harington said — coming to terms with the absence of his advisers, and his lost Wilding love, is a more complicated task.

“This is a very interesting season for him because it is about honor,” Harington said. “When he was young in the first season, honor was a simple thing. Now — in fact, in this scene — he learns that honor isn’t a simple thing. To win you have to be dirty sometimes to get to an honorable place. To eventually get to the right ending, he has to do things he doesn’t want to do. He has to leave Ygritte [Rose Leslie] and lie to her. He has to lie to his friends, he has to fight dirty at times. It was never as simple as he thought it was for Ned Stark, his idol. As he goes along he realizes life isn’t that simple, the world doesn’t treat people in the right way.

“This season is very interesting for him because he’s not got someone lecturing him, an older, patriarchal figure telling him what he should or shouldn’t do, what he should or shouldn’t think. This year, he’s on his own and he has to take all that advice he’s been given and utilize it in the right ways.”